This invention relates to a motor vehicle with a heating device for the passenger compartment, which device has a heat exchanger for exchanging heat between the engine cooling water and heating medium and to such heating devices. Known heating devices generally operate satisfactorily as long as an adequate quantity of heat is delivered to the cooling water of the engine. However, particularly in the case of high efficiency diesel engines, the quantity of heat supplied during idling and in the lower part of the load range is not sufficient to ensure adequate heating for the passenger compartment when the outside temperature is around or below freezing point. Auxiliary heat exchangers or auxiliary heating methods are independent of the engine are costly.
A device is known for heating a driver's cab, in which the heat exchanger for the heating medium is in communication with a second heat exchanger which is itself connected through a bypass line to the exhaust pipe, a control device being provided in the exhaust pipe with which the exhaust pipe can be closed, so that the exhaust gas can be passed through the second heat exchanger. The counter pressure created by the second heat exchanger loads the engine in such a way that the idling speed can be maintained only by increasing the quantity of fuel supplied to the engine. This occurs automatically in standard diesel fuel injection pumps. The combustion of extra fuel results in a corresponding increase in cooling water temperature and exhaust gas temperature. However, the provision of the second heat exchanger which is necessary for heating device and which is supposed to act as an evaporator, increases the costs of the heating device quite considerably.
The object of the injection is to provide a heating device having an adequate heat output at idling speeds and which is inexpensive.
The present invention consists in a motor vehicle, having a water-cooled engine and a heating device for the passenger compartment, which includes a heat exchanger for the heating medium connected in the cooling water circuit of the engine and a throttle element which is disposed in the exhaust of the engine which can be actuated, in a sense to restrict the exhaust manually and/or in dependence upon the outside temperature, the compartment temperature or the cooling water temperature, and which can be actuated in an opening direction in accordance with the engine load.
If the throttle element is closed manually or by a compartment thermostat or a cooling water thermostat, an increased quantity of fuel is distributed by the regulator of the diesel fuel injection pump in order to maintain the idling speed. The quantity of heat passing into the cooling water during the combustion of this extra fuel ensures adequate heating of the passenger compartment, rapid heating of the engine associated with better noise behavior in the warm running phase of the engine and low cold water.
In one embodiment of the engine, the following values have been measured for idling:
Free throttle cross-section 1.4% PA0 Consumption 190% of idling consumption with exhaust throttling PA0 Water heat 327% of the heat fed to the cooling water without any exhaust throttling PA0 Free throttle cross-section 0.9%: PA0 Consumption 224% PA0 Water heat 434%
The exhaust throttling is usually necessary only during idling and in the lower part of the load range, up to 50 km/h, and it must naturally be removed when high power is required. The throttle element is therefore preferably connected to a device which indicates the load state of the engine, for example, to the accelerator pedal or the regulating element of the fuel injection pump, in such a way that the throttle is fully opened regardless of any manual and/or thermostatic adjustment. The engine can therefore operate normally and with the lowest possible fuel consumption when a certain predetermined load is exceeded.
Additionally the throttle element can be actuatable by a brake actuator in the closing direction independently of the manual, thermostatic and/or load-dependent actuation. A controllable exhaust braking action is thereby obtained with the possibility of reducing the normal service brake. Furthermore, cooling of the engine during coasting is prevented.